This work aims to identify and characterize a specific component of executive processing and has implications regarding current debates about the organization of functions within human frontal cortex. The human frontal cortex is believed to mediate "executive processes" that are crucial for a wide variety of high-level cognitive tasks, and may be especially vulnerable to normal aging. However, the precise nature of these executive processes and their circuitry remains largely unknown. The proposed research will investigate the hypothesis that one specific function of prefrontal cortex is to mediate response selection by inhibiting competing response alternatives. This hypothesis is based on verbal working memory and semantic knowledge retrieval tasks showing activation of Brodmann's area 45, in the left hemisphere (left BA45), under conditions of high response competition. The present project has three specific goals. The first is to test the hypothesis of the function of left BA45 by neuroimaging of brain activity during novel verbal working memory tasks specifically designed to isolate and identify inhibition of response alternatives in a neuroimaging context. The second specific goal is to test the generality of the process in left BA45. Current evidence for its role come primarily from verbal tasks. We will probe working memory for faces, a specific case of object working memory. The third goal is to explore the functional relationship of left BA45 and anterior cingulate cortex, another area thought to be involved under conditions of cognitive conflict. [unreadable] [unreadable]